0. Definitions Used
Refrigeration Systems: can also include Heat Pumps and Combination Refrigeration and Heat Pump Systems
Refrigerator: can include the alternative appliances, Refrigerator/Freezer or Freezer, in appropriate contexts
Enclosure Heat Exchanger: Heat Absorber In Refrigeration Systems, Heat Supplier In Heat Pumps, Either Or Both In Combination Refrigeration/Heat Pump Systems
Surroundings Heat Exchanger: Heat Suppliers In Refrigeration Systems, Heat Absorbers In Heat Pumps
Heat Absorbers: Evaporators In Vapor Compression Systems And Absorption Systems, Cold Plates In Solid State Systems
Heat Suppliers: Condensers In Vapor Compression Systems, Refrigerant Absorbers In Absorption Systems, Hot Plates In Solid State Systems
1. Field of the Invention
The present invention relates to improved refrigeration systems, and specifically to reducing net operating costs, by increasing the effectiveness of Enclosure Heat Exchangers and, specifically in residential type refrigerators, by recovering the reject heat for heating water.
2. Prior Art
Refrigeration Systems are used for maintaining the contents of enclosed spaces at temperatures below or above the temperature of the surroundings. In some cases the functions of refrigeration and heat pumping are combined to keep the contents of one or more enclosed spaces at relatively low temperatures while also keeping the contents of one or more other enclosed spaces at relatively high temperatures. The objective is frequently to delay deterioration of the contents of the enclosed space, to maintain enclosed spaces at comfortable temperatures for occupation by humans or other animals, or to adjust the temperature of materials in preparation for use.
In the past the contents of the enclosed spaces have been maintained, at the desired temperatures, by Enclosure Heat Exchangers which exchange heat with the contents of the enclosed space. Said heat transfer is required to counteract heat which is transferred (by conduction, convection or radiation) through the enclosing walls, which are normally insulated, in addition to heat transferred along with material exchanged between the surrounding space and the enclosed space and heat generated or absorbed within the enclosed space (e.g. by chemical reaction).
Frequently the contents of said enclosed spaces include gasses, such as air, and the heat is frequently exchanged between the Enclosure Heat Exchangers and said gasses. Except during upset conditions there is frequently little or no net exchange of heat between the gaseous contents and the other contents because their temperatures tend towards equality at equilibrium.
The heat transfer coefficients between heat exchange surfaces, such as the surfaces of said Enclosure Heat Exchangers, and gasses are very low, as is well known to workers in the heat transfer field. Since the heat flow rate is approximately proportional to the product of said coefficient, the heat exchange area, and the temperature differential, it is necessary for the refrigerating means to depress or maintain the temperature of said enclosure heat exchanger so as to maintain a large temperature differential in order to drive the heat exchange between Enclosure Heat Exchangers and gaseous contents. The alternative of providing large heat transfer surfaces is limited by cost and available space. The maintenance of said large temperature differentials, for heat transfer, results in large differences between the temperatures of the Heat Supplier and the Heat Absorber of the Refrigeration System. As is well known to workers in the field of refrigeration, the efficiency of Refrigeration Systems increase as said temperature differences decrease. Consequently the maximum achievable efficiency of the Refrigeration System is very substantially affected by the fact that the heat load must be transferred between said gas and said Enclosure Heat Exchanger.
Typical residential refrigerators operate with heat absorber temperatures about 25.degree. F. below the temperature of the freezer compartment and about 60.degree. F. below the temperature of the storage cabinet. Previous efforts to reduce the effect, of said low heat transfer coefficients, on efficiency, have included the use of large and/or extended surface heat absorbers and suppliers, and forced circulation, of the gaseous contents, across the heat exchange surfaces, to increase coefficients and maintain localized temperature differentials. The use of separate refrigeration systems, for the freezer and cabinet, has been practiced by Schlussler, of Sun Frost, Arcata, Calif., to reduce the temperature difference between the storage cabinet's Heat Supplier and Heat Absorber.
Numerous other efforts have been directed towards reduced energy requirements.
These include insulation improvements, defrost cycle improvements, and compressor and fan efficiency improvements. These also tend to indirectly reduce the effect of the low heat transfer coefficients by reducing the heat load which must be transferred across the available heat exchange surface. In HVAC applications the use of variable speed high efficiency compressors and fans, and alternative heat sinks and/or reservoirs including water and the ground have been applied. Tyree (U.S. Pat. No. 4,498,306) has described a system, including enclosing means, for goods to be transported in a space to be maintained at depressed temperatures, enclosed by said enclosing means which uses means superficially similar to the present invention. Tyree describes tubes, set into the walls of transports, and attached to thermally conductive strips. Heat entering the transport through the insulated walls is "intercepted" by said strips. The heat transferred to said tubes causes refrigerant inside said tubes to evaporate. By thermosyphon, said heat is transferred to solid carbon dioxide or liquid nitrogen etc., which evaporates and is vented, thus discarding said heat to the atmosphere. Tyree's worthy objective is to control the temperature and provide uniform temperatures throughout said transport. Tyree's invention does not achieve improvement in efficiency by use of envelopment except in some extremely limited circumstances. The amount of heat absorbed by the enveloping strips and tubes is not significantly less than that which would be absorbed by a heat exchanger immersed in the atmosphere of the transport, and the amount of carbon dioxide or nitrogen evaporated is proportional to the amount of heat absorbed. Although an "immersed" type heat exchanger might have to operate at a lower temperature than would the enveloping system of strips and tubes the amount of carbon dioxide or nitrogen evaporated is not reduced as a result. The said limited circumstances in which Tyree's invention results in (the equivalent of) improved efficiency comprise circumstances where the temperature desired for the enclosed space is very slightly more than the minimum evaporation temperature of a relatively inexpensive substance such as carbon dioxide. Using Tyree's invention it is possible to achieve said desired temperature by evaporating the less expensive substance while said "immersed" type heat exchanger, which may have to operate at a lower temperature, may require that a lower boiling substance, such as liquid nitrogen be evaporated. Assuming solid or liquid carbon dioxide to be available at a lower cost per unit heat of evaporation, then Tyree's invention would result in the financial equivalent of improved efficiency relative to a heat exchanger immersed in the contents of the transport, under these, and similar, limited range circumstances.
Use has also been made of evaporator tubes, buried in the walls of refrigerator cabinets, to reduce frosting by ensuring that the cooling of the contents of the cabinet, which are frequently maintained slightly above the freezing temperature of water, does not all have to be accomplished by contacting them with a surface which is at a temperature below the freezing temperature of water. However, since this objective was accomplished without also raising the evaporator temperature, efficiency was not increased except possibly by reducing the effect on efficiency of the insulating layer of frost.
Although the above referenced contributions have improved the performance of refrigeration systems, and in some cases have increased efficiency, or in other ways reduced operating costs, none of them have achieved or fulfilled the objectives of the present invention; one of which is to reduce operating costs, by reducing the temperature difference between the heat supplier and the heat absorber, by reducing the temperature differentials required for heat transfer, by use of Enveloping Enclosure Heat Exchangers; and the second of which is by the recovery of the reject heat, specifically, from residential type refrigerators for use in meeting residential type requirements for hot water.